The excited state emissions and lifetimes of [Cr(bipy)₃]³⁺, cis – [Cr(bipy)₂Cl₂]⁺, trans – [Cr(py)₄FBr]⁺, cis – [Cr(phen)₂F₂]⁺, and trans – [Cr(py)₄F₂]⁺ were studied in hydroxylic and nonhydroxylic solvents at 77 K and as a function of temperature. The emission characteristics are determined by the relative disposition of ²E and one component of ²T₁. The energy of these two levels is influenced by intramolecular and environmental factors, and solvent-induced level inversion occurs in cis – [Cr(phen)₂F₂]⁺. The influence of temperature and solvent viscosity were studied in several glasses with variable melting ranges. The emission of all of the complexes, except [Cr(bipy)₃]³₊, were found to be influenced by solvent viscosity. This influence is large when ²E and the component of ²T₁ are close in energy, and level inversion upon melting of the solvent occurs in cis –[Cr(phen)₂F₂]⁺. The decay of the emission of Cr(III) complexes normally shows small temperature dependence at lower temperatures and large temperature dependence at higher temperatures. The threshold for the appearance of strong temperature dependence depends on intramolecular and environmental factors. The decays of all the complexes except [Cr(bipy)₃]³⁺ show strong discontinuities in the rigid-fluid transition regions of the solvent glasses which are accompanied by risetimes in the decay profiles when the emission intensity is monitored at long wavelengths. This is attributed to solvent relaxation during the excited state lifetime.

Thesis (Ph. D.)--University of Delaware, 2007. / Principal faculty advisor: Klaus H. Theopold, Dept. of Chemistry & Biochemistry. Includes bibliographical references.

Thesis (Ph. D.)--University of Delaware, 2006. / Principal faculty advisor: Klaus H. Theopold, Dept. of Chemistry and Biochemistry. Includes bibliographical references.

4-bromopyridine hydrochloride is a compound which has a relatively high formal charge on the 4 carbon. Molecular orbital calculations on pyridine show a +0.18 charge on the 4 position, a +0.15 charge on the 2 position, and a +0.05 charge on the 3 position with the nitrogen holding a -0.59 charge.12 And in aqueous acidic solutions, and added +1 charge would be distributed throughout the aromatic ring of the resulting pyridinium ion, thus increasing all charges. Benzene would show all carbons being identical having relative charges of zero each on the scale used for pyridine. As a result of these considerations, an attempt at the formation of pentaaquo-4-pyridylchromium(III) ion ensued. Information in the following sections will show success in this attempt

Anet was the first to isolate a stable sigma bonded organochromium (III) complex.1 This was the benzylpentaquochromium (III) ion obtained by the reduction of benzyl halide with chromium (II) perchlorate. The mechanism of this and similar reactions has been thoroughly studied and is believed to be2,3,4 [see PDF file for formula] where R is an alkyl group and X is a halogen other than fluorine. All complexes reported in the literature show chromium sigma bonded to an sp3hybridized carbon atom. D. Biggs, of L. Speer's research group, attempted to synthesize a complex containing chromium sigma bonded to an sp2 hybridized carbon atom.5 This was attempted by reacting chromium (II) perchlorate with parabromopyridine in the presence of N,N dimethylformamide (DMF). Amides have been shown in the literature to enhance the reductive power of chromium (II) salts.3,6,7 An orange-brown complex was obtained with Biggs attributed to parapyridylpentaaquochromium (III) ion. An attempt was made to characterized this complex, maily through the infrared (IR) and nuclear magnetic resonance (NMR) spectra of a solid mercury (II) derivative of the complex. Mercury (II) halides have been shown to react with organochromium (III) complexes via bimolecular displacement to yield the corresponding organomercury (II) halide salt which can be precipitated from solution:8,9 [see PDF file for formula] The IR and NMR spectra of a solid precipitate, obtained after the reaction of mercury (II) nitrate with the orange colored solution described above and subsequent precipitation with chloride ion, led Biggs to believe that he had prepared parapyridylpentaaquochromium (III) ion. Little effort was done to determine the stoichiometry, or the kinetics, of the aquation of the complex. The results presented here are the result of an attempt to establish the stoichiometry and the kinetics of aquation of the reported complex in acidic media. It will be shown that Biggs' assignment of parapyridylpentaaquochromium (III) as the structure of the complex is in error and another structure will be given.

published_or_final_version / Chemistry / Doctoral / Doctor of Philosophy

Thesis--Ph. D., University of Hong Kong. / Includes The Sn mechanism in inorganic reactions. Pt. I. Hydroxide-ion substitution in halogenopentamminecobalt (III) complexes, by the author and others reprinted from Journal of the Chemical Society, May, 1965. Typewritten.

The last chapter describes an extension of this cyclisation reaction enabling the synthesis of homochiral l-aryl-l,2,4,5-tetrahydrobenzazepines. The stereoselectivity observed in the acid-mediated cyclisation of homochiral N-(3,4-dimethoxyphenethyl)halostachine to Nmethyl- l-phenyl-l,2,4,5-tetrahydrobenzazepine is assessed. The chromium tricarbonyl complex of this cyclisation precursor undergoes a stereoselective cyclisation to furnish the homochiral 1-aryl benzazepine after decomplexation. The diastereoselectivity observed in the acid-mediated cyclisation of homochiral N-3,4-dimethoxyphenethyl phenylpropanolamines is also investigated and the mechanism by which they occur is discussed. Coordination of one of these precursors to the chromium tricarbonyl unit renders the cyclisation stereoselective to give homochiral N-methyl-1 -phenyl-2-methyl-7,8-dimethoxy-1,2,4,5-tetrahydrobenzazepine after decomplexation.

This thesis describes the application of (arene)Cr(CO)3 methodology to the Stereoselective and enantioselective synthesis of substituted arenes. Chapter one reviews the main methods of preparation and decomplexation of (arene)Cr(CO)₃ complexes and the electronic and steric influences of the Cr(CO)₃ unit on the arene. Chapter two demonstrates that the benzylic oxygen directing effect in complexation reactions operates via a direct oxygen bond to the incoming metal unit. Attachment of bulky ft-acceptor groups, such as t-butyldimethylsilyl, to the benzylic oxygen overrides this directing effect. Chapter three describes the regioselective Cl functionalisation of the cryptopine skeleton. Complexation of dihydrocrytopine gives only a single product, the relative configuration of the product being determined using an X-ray crystal structure analysis. Subsequent alkylation of the O-methyl derivative gives Cl alkylated products. Chapter four describes the regioselective ortho functionalisation of ephedrine and pseudoephedrine derivatives. Treatment of (1S,2R)-(N,O-dimethylpseudoephedrine) Cr(CO)₃ with n-butyllithium leads to exclusive removal of the pro-(R) ortho proton. The observed stereoselectivity arises via</em deprotonation from cyclic bidentate five-membered chelates. Chapter five describes the regioselective C4 and C5 functionalisation of (hydrocotarnine)Cr(CO)₃. Complexation of 1-methylhydrocotarnine occurs to give exclusively the exo-1-methyl derivative. Further functionalisation to give the 1,5- and 4,5-dimethyl products is also described. Chapter six describes the synthesis of ortho substituted (benzaldehyde)Cr(CO)₃ complexes. Chiral material is available via preferential kinetic hydrolysis of, or classical separation of, the L-valinol derived imines. Chapter seven describes the Stereoselective addition of nucleophiles to (o-anisaldehyde) Cr(CO)₃ and (o-trialkylsilylbenzaldehyde)Cr(CO)3. With (o-anisaldehyde)- Cr(CO)₃ the additions are completely stereoselective giving the (RR,SS) diastereoisomer. With (o-trialkylsilylbenzaldehyde)Cr(CO)₃ the ratio of products is influenced by the nature of Lewis acidic species present. Chapter eight describes the Stereoselective benzylic elaboration of (o-methoxybenzyl methyl ether)Cr(CO)₃ achieved via selective removal of the exo benzylic proton from transition states with the methoxy groups anti to each other.

This thesis deals with the applications of organopalladium and organochromium chemistry to the functionalisation of the benzopyran ring system, at a variety of oxidation levels. Section I demonstrates the functionalisation of 3-, 6-, and 8-bromochromones via palladium (0) insertion into the C-Br bond. The resultant arylpalladium species are shown to undergo addition to the least substituted end of a variety of olefins including methyl acrylate, acrylonitrile and styrene. Subsequent palladium-hydride elimination leads to overall palladium catalysed vinylation of the chromone and the synthesis of a number of novel compounds. Vinylation occurs regiospecifically at the site of chromone bromination and is shown to allow clean substituent introduction into each of the three sites. The palladium catalysed reaction of 3,6-dibromo-chromone with methyl acrylate leads to vinylation at both the C3 and C6 positions. Carbonylation of the 6-bromochromone in ethanol or butanol leads to the 6-ethyl or 6-butyl esters respectively. The palladium catalysed vinylation of the 6-bromochromone with ethyl vinyl ether leads to a mixture of products from addition of the chromone to either end of the olefin. With p-bromophenol or p-bromo-N,N-dimethylaniline the reaction gives exclusively the acetylated product arising from addition to the more substituted end of the olefin. This change in orientation is rationalised by considering the polarisation of the olefin and the arylpalladium species. Section II demonstrates the functionalisation of chroman and 4-chromanol via coordination to the Cr(CO)₃ moiety. (η⁶-Chroman)Cr(CO)₃ is synthesised and is shown to undergo regiospecific ring deprotonation at C8 under kinetic conditions or regiospecific benzylic deprotonation at C4 under thermodynamic conditions. The resultant anions are quenched with alkyl halides, aldehydes, Eschenmoser's salt and methyl disulphide resulting in selective functionalisation of either site. No mixed products are observed. The uncomplexed arene is shown to be totally unreactive under identical conditions. (η⁶-4-Chromanol)Cr(CO)₃ is synthesised and is shown to undergo regiospecific C8 ring deprotonation by comparison with authentic samples of the C5 and C8 methylated alcohols. Protection of the hydroxyl group as its methyl, t-butyldimethylsilyl or methoxymethyl ethers is found not to alter the regiochemistry of deprotonation. The 4-chromanol t-butyldimethylsilyl and tri-i-propylsilyl ethers are synthesised and coordinated to the metal unit. Cleavage of the silyl ethers is shown to proceed with loss of stereochemistry, indicating C-0 bond cleavage.